1. Technical Field
This disclosure relates to a display device reflecting ambient light, and in particular, to a display device and a method for adjusting a gray-level of an image frame depending on environment illumination.
2. Related Art
When environment illumination varies, a backlight brightness of a display device with an active backlight module, such as a liquid crystal display device, can be adjusted so that the brightness of image frame suits the environment illumination. In this way, the brightness of the image frame can be adjusted to the most suitable visual state for a user. For example, in ROC Invention Patent No. I336458 and ROC Invention Patent Publication No. TW201020606, technical features for adjusting a brightness of a display depending on environment illumination are proposed.
However, a display device reflecting ambient light, such as an electrophoretic display (e-paper), or a reflective liquid crystal display, reflects the ambient light to make image frame become visible. It is difficult for a display device reflecting ambient light to change the brightness of the external ambient light, and the display device reflecting ambient light can only reflect the ambient light passively.
Further, since the ambient light is reflected by the display device, the brightness of the reflected light is also affected by the displayed image frame. For example, under the illumination of ambient light with high brightness, if the displayed image frame has large blocks of low gray-level pixels, the brightness of the reflected light is high, so that the user feels dazzling when viewing the displayed image frame; similarly, under the irradiation of ambient light with high brightness, if the displayed image frame has large blocks of high gray-level pixels, the brightness of the reflected light generated after the ambient light is reflected is reduced, so that the user feels comfortable when viewing the display image frame.
Conversely, if the environment illumination is low and the display image frame has large blocks of high gray-level pixels, the brightness of the reflected light generated after the display-panel reflects the ambient light is reduced, so that the user cannot view the content of the display image frame clearly. Similarly, when the environment illumination is low, if the display image frame has large blocks of low gray-level pixels, the display-panel can still provide the relatively high brightness of the reflected light, so that the user views the display image frame clearly.
However, the environment illumination is an external factor and cannot be easily adjusted by the user or the display device, so that the visual effect of the display device reflecting the ambient light is easily affected by environment illumination.